Electron devices in which a GaN layer used as an electron transport layer and an AlGaN layer are disposed on a substrate, for example, compound semiconductor devices, include a GaN-based high electron mobility transistor (HEMT). In a GaN-based HEMT, a high-concentration two-dimensional electron gas (2DEG) generated at the heterojunction interface between AlGaN and GaN is used.
The bandgap of GaN is 3.4 eV, which is larger than the bandgap of Si (1.1 eV) and the bandgap of GaAs (1.4 eV). GaN has a high breakdown field strength and a high saturated electron velocity. GaN may be used as the material for a high-voltage operating and high-output compound semiconductor device, for example, the material for a semiconductor device for power supply. Compound semiconductor devices using a GaN-based compound semiconductor may be used as high-efficiency switching devices or high breakdown voltage power devices for electric cars. Si laterally diffused metal oxide semiconductor (LDMOS) transistors or GaAs field effect transistors (FETs) may not be suitable for high-output, high-efficiency, or high-voltage operation.
Related art is disclosed in Japanese Laid-open Patent Publication No, 2009-164226 and Japanese Laid-open Patent Publication No. 9-260331.